Check-in, check-out track circuit arrangement

ABSTRACT

A train approach registry relay at the exit end of the approach track section at a signal location is held normally energized over its own stick contact and releases to register the track circuit detection of an approaching train. The reenergizing circuit, when the train clears the approach section, includes a back contact of the train occupancy registry relay at the entrance end of the advance track section. Thus the train occupancy registration for the approach section is not cleared until the same train is positively detected and registered into the adjoining section. In one form, the approach registry relay is in series in the approach section signal line circuit energized over a front contact of that relay. The line circuit is reenergized, when the section is again clear, over a back contact of the advance section signal line relay. In a coded track circuit form, the approach registry relay is the reverse code decoding relay for the approach section, with its own stick front contact in the capacitor decoding network. This decoding registry relay is then reenergized by a direct circuit over a back contact of the advance section, back contact decoding relay of the master code.

United States Patent i191 in] 3,907,237

Staples Sept. 23, 1975 CHECK-IN, CHECK-OUT TRACK CIRCUIT [57] ABSTRACT ARRANGEMENT A train approach registry relay at the exit end of the Inventor: Crawford Staples, Pittsburgh, approach track section at a signal location is held nor- [73] Assignee. Westinghouse Air Brake company, mally energized over its own stick contact and releases Swissvale, Pa. to register the track circuit detection of an approaching train. The reenergizing circuit, when the train [22] Filed: May 17, 1974 clears the approach section, includes a back contact [21] Appl' NO; 470,802 of the train occupancy registry relay at the entrance end of the advance track section. Thus the train occupancy registration for the approach section is not [52] 246/34 A; 246/34 CT; 246/1 cleared until the same train is positively detected and Int. Clt registered into the adjoining ection In one fonn the of Search A, R, CT, approach registry relay is in serigs in the approach 246/41, 63 63 B section signal line circuit energized over a front contact of that relay. The line circuit is reenergized,

[56] References Cited when the section is again clear, over a back contact of UNITED STATES PATENTS the advance section signal line relay. In a coded track 2,448,570 9/1948 Allen 1246/41 circuit form the approach registry relay is the reverse 3,309,516 3/1967 Baughman 246/ 63 c x code d g r lay f r theapproach section, with its 3,401,259 9/1968 Baughman 246/34 R X own stick from contact in the capacitor decoding net- 3,552,692 1/1971 Horeczky.... 246/63 C work. This decoding registry relay is then reenergized SChatZel a direct circuit ver a back ontact the advance Primary ExaminerDuane A. Reger v Attorney, Agent, or FirmA. G. Williamson, Jr.; R. W. Mclntire, .lr.

section, back contact decoding relay of the master code.

19 Claims, 3 Drawing Figures h A3T 133 3T 1%} m AtT 133 IT Awell gm Atrei'l line Li: [$1 t U i'rli l l 15 F l 0 UP l 1 -i I l US Patent Sept. 23,1975 Sheet 1 of3 3,907,237

US Patent Sept. 23,1975 Sheet 2 of 3 3,907,237

US Patent Sept. 23,1975 Sheet 3 of 3 3,907,237

wQI L 0 En 0% u ohmbo m 5320mm m: v g lllllllll ll lll t QW M 11 km CHECK-IN, CHECK-OUT TRACK CIRCUIT ARRANGEMENT BACKGROUND OF THE .INVENTION My invention pertains to track circuit apparatus. More particularly, this invention pertains to a check-in and check-out track circuit-arrangement for use in railroad signal systems to improve the continuous detection of trains where such is a critical or difficult factor in system operation.

Although the track circuit in its various forms is the mainstay of railroad signal systems, certain difficulties in maintaining continuous train detection sometimes occur. Some of these cases are due to rust, dirt, or film on the rails and will correct themselves over a period of time or may be covered by special operating rules. However, other more serious'difficulties include the failure of light-weight trains or cars to maintain a shunt between the rails, and thus shunt the track circuit for detection purposes, due to film on the car wheels or to specific characteristics of the cars or track circuits in use. This latter type of train detection difficulty is more prevalent in rapid'transit systems where single-car or paired-car movements occur frequently and where the track circuits may be of the electronic, high frequency type. Various methods or means have been tried to improve the shunting of track circuits by single cars or light-weight trains in rapid transit operations. For example, wheel cleaners to remove the film and other train-carried auxiliary equipment to improve the rail shunt have been used with some success but not with complete assurance that train detection by rail shunt will be continuous. Accordingly, where such shunting problems exist, a check-in and check-out system is a better solution. For example, an arrangement based on existing track circuits is preferable and satisfactory. Such an arrangement can thus provide a positive detection with a type of operation readily applicable to existing or proposed signaling systems. This arrangement will be simple in operation and does not require any special type of apparatus or special indications to trains.

Accordingly, an object of my invention is an improved train detection arrangement for a railroad signaling system.

Another object of the invention is track circuit apparatus, for use in a railroad signal system, which assures continued detection of a train moving through the signaled track stretch.

A further object of my invention is a check-in, checkout track circuit arrangement for positive train detection in a railroad signal system.

Still another object of my invention is a track circuit arrangement for railroad signal systems in which a train must be detected by the track circuit detector means in an advance track section prior to the clearing of the registered train occupancy condition from the approach section.

Also an object of the invention is a railroad signaling system in which the departure of a' train from an approach section is not registered by the corresponding track circuit detection means until the same train is positively detected by the track circuit. means for the advance track section.

Yet another object of the invention is a check-in,

check-out arrangement for arailroad signaling system which requires a positive train detection by 'the advance section track circuit at a signal location before the occupancy registration of the train is cleared from the track circuit for the approach track section.

It is also an object of my invention to provide a railroad signal system 'for a stretch of track in which the approach detection of a train by the track circuit at each signal location controls the application or display of a proceed signal for that train and the detection registry is thereafter maintained, without regard for the train location even if clear of the approach section, until the same train is positively detected by the track circuit for the advance track section.

Other objects, features, and advantages of my invention will become apparent from the following specification when taken in connection with the accompanying drawings and the appended claims.

SUMMARY OF THE INVENTION In. practicing my invention, I provide for track circuit detection of trains in the sections of track between signal locations along a stretch of railway over which trains move normally in one predetermined direction. The track circuits are conventional types, specifically shown as either neutral or coded direct current (d.c.) types. However, alternating current (a.c.) track circuits can be substituted. At each signal location along the railway, train detection is provided for the track section or signal block in advance, that is, a registry of the occupancy condition of that advance section. Also, approach detection is provided for the signal section or block in approach to that specific signal location. The

approach train detection or registryrelay controls thedisplay of a proceed signal indication for, or the application of cab signal energy to, an approaching train. The approach train detection relay may be linewire controlled by neutral d.c. track circuits for registering the entry of the approaching train into the approach track section. Alternately, the approach detection may be accomplished by an approach track relay which responds to reverse code pulses where coded track circuits are in use. In this latter case, the train detection registry is specifically accomplished by a decoding repeater relay of the reverse code track relay. In either case, the approach detection registry relay is a stick relay normally held energized only by its stick circuit. Thus the release of the relay to register an approaching train interrupts the stick circuit. This approaching train occupancy registry can then only be cleared, i.e., the approach detection relay reenergized, by the registry of the positive detection of the same train by the advance section track circuit. Whateverthe type of track circuit being used, the energizing circuit for the approach train detection relay is completed by the release of the home signal relay, in response to the release of the advance track relay, to register train occupancy in the advance section. The home signal relay may either be a line relay controlled over the signal line wires or a decoding relay, in accordance with the type of track circuit in use. Release of the home signal relay, which in effect repeats the release of the advance section track relay, is a positive registry of the train into the advance section. This operation maintains a continuous detection of that train and assures that the train has entered the advance track section and that detection of the train in the approach section was not merely lost through a poor shunt. Thus, in this manner, a train occupancy indication or registration cannot be cleared from one seetion of track until the same train has been detected in a positive manner by the train detection track circuit of the advance section.

BRIEF DESCRIPTION OF THE DRAWINGS I shall now describe several specific embodiments of my invention in more detail and then define the novelty in the appended claims. During this detailed description, reference will be made from time to time to the accompanying drawings in which:

FIG. 1 is a circuit diagram of a first embodiment of my invention in which neutral d.c. track circuits and signal control line circuits are used.

FIG. 2 is a similar circuit diagram of a second embodiment of my invention in which coded track circuits also incorporating reverse track codes are used for train detection.

FIG. 3 illustrates, in circuit diagram form, modifications of the embodiment of FIG. 2 in order to supply cab signal energy for train control.

In each of the figures of the drawing, similar reference characters are used to designate similar parts of the apparatus. Standard symbols are used throughout in accordance with railraod signaling practices. All relay contact armatures, whether shown above or below the winding symbol, move upward to close front contacts when the relay winding is energized. Conversely, when the winding is deenergized, such armatures release and move downward to close back contacts. Where the relays are of a code following type and are normally operating in a coded manner, relay armature symbols are shown by dotted lines in each position to designate the normal coding operation. Biased relays are designated by an arrow shown within the winding symbol with the direction of the arrow indicating the conventional current direction required for properly energizing the relay winding to actuate a response by the armatures to close front contacts. Relays provided with inherent slow acting characteristics are designated by an arrow drawn through each contact armature with the point of the arrow indicating the direction of slow operation. For example, for a slow pickup relay, the arrow symbol will point upwards indicating a delay in the closing of front contacts after the relay winding is energized. Snubs are provided on relay windings where a slight delay in contact release is required but such relays are not designated as slow release. As illustrated in the drawings, these snubs comprise diodes or resistor-capacitor circuits which function in a well known manner. In each circuit arrangement, a local source of direct current energy for supplying the relays is provided. Such direct current sources are conventional and any one of several types may be used. Thus no specific source is shown but connections to the positive and negative terminals thereof are designated by the conventional reference characters B and N, respectively. Where an energy supply for cab signal purposes is required, an alternating current source of suitable voltage and frequency for the cab signals in use is designated by the terminals BX and NX.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Referring now to FIG. 1, across the top are shown the two rails 11 and 12 of a stretch of railroad track over which trains normally move from right to left. These rails are made electrically continuous in any normal manner except where divided into track sections by the various sets of insulated joints l3. Representations of two complete track sections ST and AlT are shown with a section A3T extending off the drawing to the left and a section 1T extending to the right from the drawing. A wayside signal 38, illustrated by conventional symbol, is located at the junction between adjoining sections 3T and AlT at the center of the drawing. This signal governs train moves from section AlT into section ST and beyond. Although any known type of wayside signal can be used with my system, specifically a 3 unit, color light signal is assumed with the three lamp symbols illustrated at the bottom of the drawing connected by a dash line from the conventional symbol along the track representation. The conventional three lamps are a green lamp G, a yellow lamp Y, and a red lamp R which, as is known, provide a clear, caution or approach, and stop signal respectively.

Each track section is equipped with a track circuit, which in this embodiment is specifically of the d.c. neutral type. For example, section AlT is provided with a track circuit which includes a track battery AlTB connected across the rails with a series resistor at the righthand or distant end of the section and a track relay AlTR connected across the rails at the end of the section adjacent wayside signal 38. Relay AlTR is energized and picked up when no train is occupying any portion of the corresponding track section and conversely is deenergized and releases when a train shunt exists between the rails at any point within the track section. A similar track circuit for section 3T includes track battery 3TB and track relay 3TR connected across the rails of the section at the distant and near ends, with respect to signal 38, respectively. Sections A3T and IT are provided with equivalent track circuits of which only the track battery is illustrated, connected across the rails of these sections adjacent the correspondingly numbered complete sections. For each of these latter two track sections, the track relay is connected across the rails at the distant, unillustrated end of the track section. It is assumed for purposes of this description that the next wayside signal in advance of that shown, that is, in the direction of train movement, is at the distant end of section A3T. Conversely the nearest signal in approach to signal 38 is at the distant end of section 1T. Thus the approach signal block includes both track sections IT and AlT while the signal block in advance of signal 35 includes sections 3T and A3T. It is relatively common and conventional practice, where d.c. neutral track circuits are in use, to have more than one track circuit within each signal block. The apparatus and local circuits at each adjacent wayside signal location are similar to those shown at the location of signal 35.

Extending each direction from the signal location is a separate two wire, polarized line circuit for signal control purposes. Only the local portion of each line circuit at signal 38 is specifically shown but the full details of either line circuit may be determined from the two end portions shown which represent the opposite ends of any one line circuit. Considering in more detail the portion of the line circuit extending from the advance signal location to the location of signs] 38, the circuit includes line wires 14 and 15, front contacts a and b of track relay 3TR, and the winding of the home and distant signal relay 3HD. Relay 3I-ID is a polarized type of relay which also includes neutral contacts which operate regardless of the polarity of the current flowing through the relay winding. Only one polar contact is illustrated, the bottom contact e for which the armature is illustrated in a vertical direction so that it operates to close right or left contacts depending upon the direction of the current flowing through the relay winding. When any current flows so that the winding is energized, all other contacts of this relay are picked up to close front contacts in a normal manner. The polarity of the energy supplied over line wires 14 and 15 is determined at the advance signal location in a manner which will become apparent shortly.

Originating at the illustrated signal location and extending to the signal location in approach is another line circuit including line wires 16 and 17, front contacts a and b of track relay AlTR, contacts a and b of relay 3HD, the winding of an approach detector or registry relay lAP as well as its front contact a, which is in multiple with back contact c of relay 3HD. It is to be noted that in this circuit, regardless of the position of relay 3HD, the polarity of the energy being applied to the winding of relay lAP is the same so that its contacts are picked up or released only as the circuit is complete or open, respectively. In the illustrated condition, with relays 3I-ID and IAP previously energized, energy is supplied to this right line circuit from terminal B of the local source over front contact a and through the winding of relay lAP, thence over front contact a of relay 3I-ID and front contact a of relay AlTR to line wire 16. The return path from line wire 17 is over front contacts b of relays AITR and 3I-ID to terminal N of the local source. When relay 3HD is deenergized so that its back contacts are closed, the polarity of the energy applied on lines 16 and 17 is reversed with the connection from terminal B over front contact a and through the winding of relay IAP extending over back contact b of relay 3HD and front contact b of relay AlTR to line wire 17, returning from wire 16 to terminal N over front contact a of relay AlTR and back contact a of relay 3HD. The line circuit including wires 16 and 17 terminates at the approach signal location at the distant end of section 1T through front contacts of the section track relay lTR (not shown) and the winding of a polar relay similar to relay 3HD. Thus this line circuit is interrupted when an approaching train occupies section 1T so that the corresponding track relay releases. With either this relay lTR or the illustrated relay AlTR shunted and released, relay lAP is deenergized and releases. It is to be noted that when relay lAP releases to open its front contact a, it cannot be reenergized over its own front contact but can only be'reenergized when the line circuit including wires 16 and 17 is again complete and energy is supplied from terminal B over back contact c of relay 3HD.

The lamps of signal 38 are controlled by a circuit network including contacts of relays 1A? and 3HD. L'amps G and Y of the signal are controlled by a circuit between terminals B and N of the local source which includes front contact d of relay 3I-ID, back contact b of relay lAP and, for lamp G, the left or normal contact e of relay 3I-ID while for lamp Y the right or reverse contact of relay 3HD is closed. It will be obvious that neither of these proceed indications on the signal are actually displayed until an approaching train is detected in the signal block including sections IT and AlT so that relay lAP is deenergized and releases to close its back contact b, thus registering train occupancy of the approach block. When this train enters track section 3T, relay 3TR releases, opening its front contacts a and b to interrupt the incoming signal line wires 14 and 15 so that relay 3l-ID is deenergized and releases to register a train occupancy in the advance block. The closing of back contact d of this latter relay completes the simple circuit for energizing lamp R of signal 35 which thus displays the red or stop indication behind the train. At the same time, the closing of back contact c or relay 3HD prepares a circuit path for reenergizing the line circuit extending to the right including line wires 16 and 17.

When the train departs from section AlT so that relay AlTR picks up, the closing of its front contacts a and b completes this line: circuit further including back contact 0 of relay 3I-ID and, in the polarity changing portion, back contacts a and b of this relay. This also energizes the winding'of relay 1A? which then picks up, closing its front contact a to complete the stick circuit path to hold relay lAP and the line circuit energized when relay 3I-IDsubsequently picks up. This application of energy to line wires 16 and 17 energizes the HD relay at the distant end of section IT and thus enables the display of a proceed signal indication on the approach signal at that location. It is apparent, then, that only when the train moving through this stretch is detected by the track circuit for section 3T, so that relay 3TR releases followed shortly by the release of relay 3HD, can the train occupancy registration be cleared from the signal block in approach to signal 38, that is, the block including sections AlT and IT. This is accomplished by reenergizing relay 1A? and the line circuit including wires l6 and 17 over back contact c of relay 3HD as previously described.

Referring now to FIG. 2, a similar signal location is shown at the junction of two track sections IT and 3T. Each section extends to the next signal location in that direction since the use of coded track circuits enables a single track circuit to detect trains over the entire distance of the signal block. Signal 3S, shown by conventional symbol along the wayside with the lamps shown below for the assumed color light signal, is similar to that previously shown and iscont'rolled by a circuit network which will shortly be discussed. In each track circuit, coded energy is transmitted alternately in each direction with master code pulses flowing from left to right while reverse code pulsesv return in the opposite direction. Since each signal location along the stretch of track is provided with equivalent apparatus, the complete track circuit arrangement for either section 3T or IT will be apparent from a review of the circuits shown in FIG. 2. In other words, corresponding apparatus is located at the other end of each track section.

In keeping with the above discussion, at the entrance end of section 3T, the track' circuit apparatus illustrated receives master code pulses transmitted from the distant end of section 3T and in return transmits reverse code pulses, in the direction from right to left, to the associated apparatus at the distant end. Track relay 3TR, illustrated as a biased relay with the correct current flow being from right to left through the relay winding, is normally energized at the beginning of a master code pulse reception over the circuit from rail 11 through the winding of relay 3TR and over back contact a of reverse code transmitting relay 3RC to rail 12. Since the flow of energy is perselected to be in the proper direction, relay 3TR picks up and closes its front contact a to complete a brief stick circuit which holds the relay energized during the remainder of the master code pulse, bypassing back contact a of relay Relay 3RC is also a biased relay and is controlled by a simple circuit including front contact b of relay 3TR which periodically applies energy from terminals B and N of the local source to the winding of the relay. A diode snub on the relay winding slightly retards the release of relay RC, when front contact b of relay 3TR opens, for purposes of better coding operation; Since contact b of relay 3TR, which is following master code pulses under normal conditions, is alternately closing front and back contacts, the armature is shown dotted in both positions to illustrate this normal code following operation. When reception of a master code pulse terminates so that relay 3TR releases, the circuit is then completed which extends from rail 12 through track battery 3TRB and a series resistor, over front contact b of relay 3RC and back contact a of relay 3TR, and through the winding of relay 3TR in the reverse direction to rail 11. A reverse code pulse is thus transmitted duringtheopen circuit or off time of the master code pulses. Since relay 3RC is deenergized when relay 3TR releases and is held picked up for only a brief period by the diode snub before the circuit including back contact b of relay 3TR closes, reverse code pulses are normally of shorter duration than the master code pulses transmitted from the other end of the section. This reverse code pulse transmission is well known in the railway signaling and coded trackcircuit arts and the brief explanation here given is sufficient for an understanding of such operation.

A train occupying section 3T will be detected by relay 3TR remaining released but the track section occupancy is actually registered by front and back contact repeaters of relay 3TR, the decoding relays 3TFP and 3H, respectively. This is a well known decoding arrangement and a brief explanation only will suffice. For convenience, the decoding circuit is energized over contact c of relay 3RC rather than directly over a code following contact of the track relay. However, since relay 3RC is directly repeating the operation of relay 3TR, an equivalent decoding function results. The front contact repeater relay 3TFP is energized each time front contact 6 of relay RC closes during its code following operation. It will be noted that the relay 3TFP winding is snubbed by a diode to enable this relay, once picked up, to bridge the deenergized periods between the periodc closing of front contact of relay 3RC. The home signal or back contact repeater relay 3H is energized by a circuit from terminal B over back' contact 0 of relay 3RC and front contact a of relay 3TFP through the winding of relay 3H and over the mechanically tuned back contact 0 of relay 3TR to terminal N. This last contact, as noted by the slash line drawn through the terminal of the armature and designated by the refernece 180, is a mechanically resonant contact which follows the operation of relay 3TR to alternately close front and back contacts only when relay 3TR is receiving code pulses at the designated code rate of 180 pulses pre minute. However, since contact 0 of relay 3TR will remain closed in its back position when any other code rate is being received, relay 3H acts as a back contact repeater of any code following operation of relay 3TR through the direct repeater action of relay 3RC. Relay 3H is provided with a snub,

comprising a capacitor and resistor series circuit, connected to shunt the winding of relay 3H over front contacts a and b of relay 3TFP to bridge the code following operation of relay 3RC. Relay 3H also has slow pick up characteristics to avoid registering code reception if only two or three pulses are inadvertently received by relay 3TR.

At the exit end of section 1T, the master code pulses for that section are transmitted by the illustrated apparatus while it receives the reverse code pulses transmitted from the other end by apparatus similar to that just discussed for section ST. The approach track relay lAR, a biased relay similar to other track relays such as 3TR, is connected across rails 12 and 11 for receiving reverse code pulses over back contact a of code transmitter repeater relay CTP. When front contact a of relay CTP is closed, a master code pulse is transmitted from track battery 1TB through the rails 11 and 12 to the distant end of section 1T. Since the master code pulse rate determines also what the reverse code pulse rate will be, relay CTP has always released to terminate a'master code pulse before the reverse code pulse is received to energize relay lAR so that the alternate transmitting and receiving of code pulses proceeds without any overlap problem. The code following operation of relay lAR isdecoded by a well known capacitor decoding arrangement which includes the approach repeater relay 'lAP. Under normal conditions, as shown, a capacitor C1 is charged each time relay lAR picks up to close its front contact aby a circuit extending between terminals B and N of the local source and further including stick front contact a of relay lAP. When relay lAR releases at the end of each code pulse reception, the closing of its back contact a provides a discharge path for capacitor C1 through the winding of relay lAP and the common connection to the negative terminal N of the source. Relay 1A? is sufficiently energized by this pulsating energy to remain picked up. The winding of this relay is snubbed by a diode to provide sufficient slow release to bridge the normal coding operation of contact a of relay lAR. Relay lAP thus registers the track occupancy'condition of section IT at this exit end andis designated an approach train registry relay. It will be noted that, once release by train occupancy, relay lAP cannot be reenergized by its normal decoding circuit since its front contact a will be open to interrupt the charging circuit for capacitor C1. Under these conditions, an energizing circuit exists from terminal B over back contact a of relay 3H and through the winding of relay 1A? to terminal N. Once picked up by this energizing circuit, relay lAP closes its front contact a to reconstitute the decoding network.

To the right of relay lAP is shown a code transmitter device designated CT. Several well known devices of this type exist and any one may be used. As illustrated conventionally, code transmitter CT has two contacts which, with th'e device continuously energized, periodically close front contacts at code rates of and times per minute as designated by the numbers associ ated with these two contacts. Separate code transmitters' for each code rate can be used if preferred. Code transmitter repeater relay CTP then is controlled by one circuit which includes back contact b of relay 3H, the 75 code rate contact of device CT, back contact b of relay IAR, and the winding of relay CTP. When from contact b of relay 3H is closed, a second circuit extending from terminal B at that contact includes front contact c of relay lAP, the 180 code rate contact of device CT, back contact b of relay lAR, and the winding of relay CTP to terminal N. Obviously then, the master code transmitted from this location through section IT is at the 75 code rate when section 3T is occupied and relay 3H thus released. When section 3T is not occupied so that code pulses are received and decoding relays actuated, the closing of front contact b of relay 3H, providing relay lAP has been reenergized, selects the 180 code rate contact of transmitter CT and pulses at this rate are then transmitted. By this last described circuit, it is apparent that the 180 or clear code rate cannot be transmitted through section 1T unless relay lAP has been reenergized and picked up to positively indicate that, having vacated section 1T, the train was detected in, and has moved out of section 3T.

Master code pulses at the 180 code rate are decoded in the illustrated apparatus associated with section 3T by the distant signal relay 3D. This relay is energized by a circuit including front contact a of relay 3H, the relay winding, back contact b of relay lAp, and the front contact of the 180 decoding contact c of track relay 3TR. As previously explained, contact c of relay 3TR operates between its front and back positions only when the relay winding is energized by code pulses at the 180 code rate. The winding of relay 3D is snubbed by a diode, while front contact a of relay 31-1 is closed, to provide sufficient slow release to bridge the coding operation of contact c of relay 3TR. Further, it will be noted that relay 3D is not energized unless a train has been detected approaching through section IT, as registered by the release of relay lAP to close its back contact b. Thus the green lamp G of signal 38 is not energized to display a clear indication until relay 3D picks up, completing the circuit including front contact a of this relay, back contact d of relay lAP to again assure that an approaching train has been detected, and front contact of relay 3H, which indicates that section 3T is clear of any train. If a lesser code rate is being received, so that relay 3D is released, its back contact a shifts this energizing circuit to the yellow lamp Y of signal 3S. When track section ST is occupied so that relay 3H is released and its back contact 0 closed, a simple circuit over this contact is completed for energizing the red lamp R of signal 3S. Once again in this embodiment, a proceed signal is not displayed by signal 38 until a train is detected as approaching through section 1T. Also included by the arrangement of my invention are other forms of decoding, such as tuned resonant units for decoding the 180 code rate and other possible circuit arrangements for decoding the slower or 75 code rate, all known in the art.

Describing the operation of the apparatus in FIG. 2, it is first assumed that no trains are occupying either of the track circuits illustrated. Thus all the relays at signal location 38 at the junction between these two ad-- joining sections are in the condition shown in the drawing. When a train enters the distant end of section 1T, the reverse code pulses transmitted from that location are shunted through the. axles and wheels of the train so that relay lAR no longer receives code pulses and remains released. Since the relay-RC at that distant location will shortly cease operation, it will be evident from the apparatus shown at signal 38 that the transmission of the reverse code pulses will also shortly be completely interrupted. However, relay CTP continues for the moment to follow code under control of transmitter CT and causes master code pulses to be transmitted through the rails to the train shunt. Since no pulses are being received, relay lAP shortly releases and opens its stick circuit at its own front contact a. The opening of front contact 0 of relay lAP interrupts the 180'code control circuit for relay CTP so that, if relay 31-1 is picked up, the operation of relay CTP now ceases. The closing of back contact b of relay lAP completes the circuit for relay 3D, providing that relay 3H is picked up and relay 3TR is operating at the 180 code rate. Relay 3D picks up at this time under these conditions to complete the circuit for the green lamp of signal 38 since back contact d of relay lAP also closes. If relay 3D is not energized, then the yellow lamp Y of signal 38 will be energized. These conditions continue to exist as the train approaches through section 1T.

When the train accepts the proceed indication on signal 3S and enters section 3T, its wheels and axles shunt across the rails and deenergize relay 3TR, which then remains in its released position. This deenergizes relay 3D which shortly releases. Relay 3RC also remains released since there is no coding action by contact b of relay 3TR. With relay 3RC holding in its released position, no reverse code pulses are transmitted. Relay 3TFP is also deenergized and shortly releases, since the diode snub will not hold it energized for a long period, to open its front contacts a and b. This in turn interrupts the circuit for relay 3H which shortly releases, especially since the opening of front contact b of. relay 3TFP has interrupted the snub shunting the winding of relay 3H so that its release period is shortened. When relay 3H releases, it closes its back contact c to apply energy to the red lamp of signal 38 so that a stop indication is displayed to any following train. The opening of front contact 0 of relay 3H obviously interrupts all circuits for energizing any other lamp of this signal. Contact b of relay 3H shifts the circuit for energizing relay CTP to the code rate contact of transmitter CT and, since back contact b of relay lAR remains closed, the circuit is completed for relay CTP to operate at this slower code rate. Transmission of the master code pulse in section IT at this 75 code ratebegins at this time since contact a of relay CTP periodicallycloses in its front position. However, as long as the train shunt exists, there is no other result from the transmission of these code pulses. The opening of front contact a of relay 3H also interrupts the connection from terminal B to the winding of relay 3D and assures that this relay remains released. The closing of back contact a of relay 3H completes the reenergizing circuit for relay lAP which then picks up under steady energy since this circuit remains closed. Thus the assured detection and registry of the train in section 3T, as indicated by the release of relay 3H as the result of the shunting of track relay 3TR, allows the approach train registry relay 1A? to be restored to its picked up, i.e., non-occupied, condition. When this train clears section 1T, master code pulses at the 75 rate are transmitted to the other end. Reverse pulses are again transmitted and received at the location of signal 38 so that relay lAR again follows code pulses. Capacitor Cl is then periodically energized when front contact a of relay lAR closes since front contact a of relay 1A? is already closed. Thus the conditions are prepared whereby relay lAP may be retained energized over its stick circuit when relay 3H again picks up after the train has cleared section 3T. It is to be noted that, if the train shunt was not effective in section 3T, that is, relay 3TR continues to follow code pulses, relay 3H will remain picked up. Under these conditions, relay lAP cannot be reenergized, even if relay IAR again follows code, because front contact a or relay lAP remains open so that no decoding energy can ever reach capacitor C1. Under these conditions, i.e., the absence of the train shunt in section 3T with relay 3H picked up, the 180 code rate contact of transmitter CT will be selected but, since front contact of relay 1A? is open, relay CTP cannot be energized at the code rate. With back contact a or relay CTP remaining closed, no master code will be transmitted through section 1T. Even if relay IAR is energized by code pulses, either of foreign current induced into the rails or because of loss of the train shunt, under these conditions there can be no code transmission through section lT of master code pulses. Thus relay lAP retains the occupancy registry for section IT and no other train can approach except possibly at a restricted or very slow speed authorized by train order. Again in this embodiment, therefore, the registry of a train in a track section is retained until a positive detection of that train occurs in the advance section. In other words, the train registry relay lAP is reenergized, to clear a train occupancy registration from section 1T, only by the registry of the train detection for the advanced section as indicated here by the release of relay 3H.

Turning now to FIG. 3, an embodiment is shown in which cab signals are provided on board the train but no wayside signals are installed. Thus, although the insulated joints 13 shown in the center of FIG. 3 represent the same junction between the sections 3T and IT as previously illustrated, there is no wayside signal symbol at this junction since such signals are not provided. Coded track circuits similar to those used in FIG. 2 are used, with minor variations since cab signals only and no wayside signals are controlled. What might be termed spot'detection by a proximity detector and a timing period to aboid premature application of cab signal energy are added to the arrangement. However, this proximity detection and the timing periods are not absolutely required for a cab signal only arrangement as here illustrated which provides for a one block overlap between train. But if trains normally follow closely, for example as under the short headway conditions often used in rapid transit systems, the added protection of the additional detection devices and timing period is an advantage since it will cover and provide protection under track circuit failure conditions.

For the proximity detector, a relatively short track loop, illustrated by the dash lines 18 and on the order of to feet in length, is installed parallel to the rails just inside section 3T, that is, just to the left of the insulated joints 13. The loop may be relatively short since the purpose of the proximity detector is to assure that the rear of the train at least has cleared the.section junction point, that is, joints 13, by a nominal and relatively short distance and that no cars have been left at the junction which are not shunting across therails. Several conventional types of proximity detectors are known and have been used in the railroad signal art. Thus only a conventional block designated as a proximity detector is shown. The apparatus may be, for example, as shown in U.S. Pat. No. 2,537,298, issued to G.

W. Baughman on Jan. 9, 1951 for Traffic Controlling Apparatus. However, in the present installation, no coding of the proximity detector energy is needed since the operation is otherwise checked. It is sufficient to understand that the proximity detector relay 3PD is normally energized by the proximity detector apparatus when no train is occupying the portion of the rails parallel to loop 18. Relay 3PD is deenergized and re leases when the train is within the loop area. This relay is made slow acting, that is, slow pickup, to delay its operation to protect against any false energization of the relay by induced pulses while a train is still in the loop area. A slow release repeater relay 3PDP is provided which is energized to indicate the release of relay 3PD by a simple circuit including back contact a of relay 3PD. The purpose of the slow release characteristics for this relay, indicated by the downward pointing arrow, will become apparent in the following discussion.

The time delay apparatus and network includes two relays, the time element stick relay TES and a time element relay TE. This latter relay may be any one of several types known in the signaling art which, when the winding is energized, do not pick up to close normal front contacts for a preset timing period which may be of any length in the range from 30 seconds up to at least 5 minutes. A slow pickup front contact is illustrated by contact a of relay TE with the upward pointing arrow drawn through the armature portion of the contact. Contact b of relay TE is of the type known as a checking back contact which immediately opens when the relay winding is energized and is not involved in the timing period. Relay TES is provided with two stick circuits, the first of which includes front contact a and the winding of relay TES and parallel connections to terminal B over front contacts c of the home signal relay 3H and the proximity detector repeater relay. 3PDP. This first stick circuit is normally retained closed by front contact 0 of relay 3H. A second stick circuit for relay TES includes the winding and front contact b of relay TES and front contact c of relay 3PD which is normally closed. Obviously, relay TES is normally energized over both of these stick circuits. Once deenergized, relay TES releases quickly and can then only be reenergized by a pickup circuit including front contact c of relay 3PD, front timing contact a of relay TE, and the winding of relay TES. The energizing circuit for relay TE includes front contact 0 of relay 3PD, back contact b of relay TES, and the winding of relay TE. Thus the time element relay is energized, after relay TES has released, when no portion of a train is occupying the stretch of track parallel to loop 18 of the proximity detector so that, registering the absence of a train, relay 3PD picks up to close its front contact 0. Obviously, when relay TE completes its timing period and closes its front contact a, it then completes the circuit to reenergize relay TEX. When this occurs, relay TE is immediately deenergized and releases, opening its front contact a and once again closing its back contact b which opened immediately upon the energization of the relay winding, as previously described.

The circuits associated with section 3T for receiving the master code pulses from the other end and for transmitting the reverse code pulses through the section are very similar to those already described for FIG. 2 and operate in relatively the same manner. One exception is that relay 3RC receives energy for its operation over front contact a of relay 3H and thence over the periodically closed front contact b of relay STR. Front contact a of relay 3H is included for an additional check since the decoding circuitry about to be described is based on the coding contacts of relay 3TR rather than those of relay 3RC. In other words, 'the circuit for energizing front contact repeater relay 3TFP extends from terminal B at front contact a of relay 3PD over periodically closed front contact of relay 3TR and back contact a of relay 3PDP through the winding of relay 3TFP to terminal N. Likewise, energy for the home signal relay 3H, the back contact repeater of the track relay, is supplied over the same front contact a of relay 3PD with the circuit then extending over back contact c of relay 3TR, periodically closed during coding, front contact a of relay 3TFP to check that the front contact repeater is picked up, and thence through the winding of relay 3H to terminal N. The diode shunt on the winding of relay 3TFP, to provide a slight delay in its release, is connected so as to include back contact a of relay 3PDP in the snub circuit, which thus is interrupted so that front contact repeater 3TFP quickly releases when the proximity detector detectsthe presence of a car within the loop area. Front contact a of relay 3PD interrupts the decoding circuitry so that there can be no decoding of any code following operation of 3TR which might result if a car occupying the loop 18 area was not shunting the rails so that master code pulses were being received by the track relay. Al though more cab signal indications can be provided if desired, for convenience in the drawing arrangement cab signal energy is shown as being only on or off so that only proceed or restricted cab signal indications are provided. Thus only a single code rate is used and no distant signal relay such as relay 3D of FIG. 2 is needed in the decoding operation of the master code reception by relay 3TR. In other words, a simple front and back contact repeater decoding of the operation of relay 3TR is sufficient in the arrangement illustrated.

The code receiving and transmitting circuits at the exit end of section 1T are somewhat varied from those described for the FIG. 2 arrangement. For one thing, the approach track relay lAR is a two winding relay, each of which is provided with biased characteristics. The upper winding is connected across the rails of section 1T over back contact a of code transmitter repeater relay CTP to receive the reverse code pulses transmitted from the distant end of section IT. This circuit controls the pickup of the approach track relay while the lower winding is used only to smooth the code following operation of this relay and has a stick circuit which includes back contact a of a code transmitter CT and front contact b of relay lAR. The decoding relay or train occupancy register relay lAP is controlled by a capacitor decoding circuit much in the same manner as previously described in connection with FIG. 2. Capacitor Cl is periodically charged when back contact a of relay lAR closes during its code following operation to complete a circuit between terminals B and N through capacitor Cl. When front contact a of relay lAR closes, the circuit is completed for discharging capacitor Cl through the winding and stick front contact a of relay lAP. When relay lAP releases to register the detection of an approaching train, due to the lack of any code following operation by relay lAR, it cannot be reenergized until its pickup circuit is completed. This latter circuit extends from terminal B over back contact a of relay 3H, which releases to close this back contact when the train is detected occupying section 3T, and front contacts b, in series, of relays SPD and 3PDP to the winding of relay lAP. It will be noted that this pickup circuit exists only during the slow release time of relay 3PDPwhich commences as soon as relay 3PD picks up to close its front contacts and thus interrupt the energizing circuit for relay 3PDP. lf relay 1A? is not energized during this time, perhaps because back contact a of relay 3H is not closed, then it cannot be picked up and the track circuit apparatus for section 1T cannot reset under these conditions.

The code pulse transmission circuits are also varied to provide for the cab signal energy transmission. A single pulse rate code transmitter CT is permanently connected across the terminals of the local source. The circuit for its repeater relay CTP then is traced from terminal B over back contact b of track relay lAR, from contact a of code transmitter CT, and the winding of relay CTP to terminal N. The single code rate at which contact a of transmitter CT operates may be, for example, pulses per minute. However, other code rates may be used if desired. It will be noted that relay CTP can only pick up when relay lAR is released so that there can be no overlap of master and reverse code pulses. Since the master pulses as fixed by transmitter CT and repeated by relay CTP determine also the rate of the reverse code pulses, the interconnection of the energizing circuit for relay CTP with the energizing circuit for the lower winding of relay lAR, as previously traced, is a convenient and conventional arrangement for smoothing the transmission of code pulses and for regulating the effective on-time of the received reverse code pulses, as marked by the pickup of relay lAR.

The direct current master code pulse is normally transmitted and developed in the circuit traced from the positive terminal of track battery 1TB through the series resistor and over front contact 0 of relay lAP and front contact a of relay CT? to rail 12, returning from rail 11 to the other terminal of the track battery. The code rate, of course, is fixed by the code following operation of contact a of relay. CTP. When relay lAP releases upon detection of a -train.approaching through section 1T, its contact c closes in the back position to interrupt the transmission of direct current pulses but substitute in their place alternating current energy from the secondary winding of a track or cab signal transformer CS. As with the regular master code pulses, contact a of relay CTP again codes the transmission of the cab signal energy into therails. The primary winding of transformer CS is supplied with alternating current energy of the cab signal "frequency by a circuit which may be traced from terminal BX of that source over the checking back contact b of relay TE, front contact 0 of relay TES, front contact b of relay 3H, back contact b of relay lAP, and the primary winding to the other terminal NX of the source. Obviously this transformer CS is energized only when a train is detected approaching through section 1T, registered by back contact b of relay lAP, and will not be transmitted if relay 3H is released to open its front contact b, indicating that a train is occupying some portion of section 3T. This latter check provides the one block overlap in cab signal energy to provide additional protection between trains moving along the track.

It has been noted that the arrangement shown in FIG. 3, for providing a cab signal energy for the operation of the trains, may be installed without a proximity detector and timing delay arrangement or alternately may be installed with a proximity detector arrangement but without any timing delay. However, the following operational description will include both of these additional features although occasional mention will be made of the type of operation occurring without such additional protection. It is initially assumed that no train is occupying any portion of sections IT or 3T so that all apparatus shown in FIG. 3 is in the condition or position illustrated. In other words, direct current master code pulses are being received by track relay 3TR, decoded, and reverse code pulses transmitter by relay 3RC. Also direct current master code pulses are being transmitted through track section IT by the operation of relay CTP. Reverse code pulses are received from the other end to which relay lAR responds and its operation is decoded to provide energization of relay lAP. When a train enters the distant end of section 1T, it is detected as approaching by the fact that no reverse code pulses are now received by relay lAR which remainsin-its released position. Relay IA? is thus deenergized and shortly releases to open the stick circuit over its own front contact a. Relay CTP continues to follow theoperation of transmitter CT even though relay lAR remains released since the circuit for relay CTP is thus supplied with energy over continuously closed back contact b of relay lAR. The closing of back contact b of relay lAP applies cab signal energy to the primary of transformer CS and back contact of relay lAP connects the secondary of this transformer to the railsover contact aof relay CTP. This applies coded energy to the rails for the operation of the cab-signals in the approaching train. Thus the cab signal operation depends upon the approach detection of the train and reception of such signal energy and the display of the cab signal assures the train operator that the train shunt is effective between the rails of section 1T. As will become apparent from the following discussiomthe train operator is also assured that no cab signal energy will be supplied to the track sectionimmediately to the rear of his train so that he is protected by a signal block overlap arrangement from a rear end collision.

There is no further changein the apparatus until the train enters section 3T and shunts the rails. Track relay 3TR then remains released in response to the train shunt. Relay 3RC also remains released and relays 3TFP and 3H shortly release following the halt in code operation. of relay 3TR. The opening of front contact b of relay 3H opens the connection from terminal BX so that cab signal energy is no longer supplied to section 1T. It may be noted at this point that it is the release of relay 3H which registers the occupancy of section 3T by this train. Relay 3PD also releases when the proximity detector responds to the presence of the train within the loop 18 area and relay 3PDP is energized and picks up. Front contact c of relay 3PDP closes prior to the opening of front contact 0 of relay 3H so-that the first stick circuit for relay TES remains complete and this relay is held energized. It is to be noted that the second stick circuit for relay TES opens section ST and relay 3TR cannot pick up since d.c. code pulses are not present even if the train'shunt is at times intermittent. Once again, upon receipt of a proceed cab signal indication, the train'operator is assured that his train has shunted the rails of section ST and that no cab signal energy is being applied in section IT to the rear of his train.-

The train shortly clears section IT and then quickly thereafter loop 18 of the proximity detector apparatus. Relay 3PD then picks up, at theend of its slow pickup period, deenergizing the winding of relay SPDP which begins its slow release period. During this slow release period, the circuit including back contact a of relay 3H and front contacts b of relays SPD and its repeater 3PDP is complete for reenergizing the winding of relay 1A? which then picks up. The pickup of relay lAP transfers, at its contact c, the track circuit connections from the secondary of transformer CS to track battery 1TB so that master code pulses are again transmitted. Correspondingreverse code pulses are shortly received from the distant end of the section and relay lAR follows such pulses. Relay lAP then receives decoding energyfrom capacitor C1 over the normal circuit including its own front contact a so that it is held energized upon the release of relay 3PDP. If the train should halt so that it is standing over loop 18, or if it inadvertently leaves one or more cars behind, the proximity detector holds relay lAP deenergized since front contact b of relay 3PD does not close to complete the energizing circuit. It is also to be noted that, if a following train enters section 1T prior to the leading train clearing section 3T,'relay lAR again ceases operation and relay lAP releases since its pickup circuit will be open at front-contact b of relay 3PDP. However, no cab signal energy is applied for this following train upon its detection since the circuit for supplying energy to the primary of transformer CS isopen at front contact b of relay 3H. This once again illustrates that a full signal block overlap protection represented by the approach track section to the junction shown, exists between trains through the control of the application of cab signal energy. The second train would be required to proceed at restricted or slow speed through section 1T so that it would be able to stop short of a preceding train or prior to entering section 3T.

If this second train should be authorized, still at slow speed, to enter section 3T behind the first train, relay 3H is still released since relay 3TR is not receiving code pulses. When the proximity detector detects this second train, the release of relay 3PD to open its front contact c will then deenergize relay TES since front contact 0 of relay 3H is already open. This deenergization of relay TES- by the interruption of its second stick circuit occurs before relay 3PDP can pick up to close its front contact c to again complete the first stick circuit. Relay TES then releases, opening its front contacts a, b,-and c, which further interrupts both stick circuits so that the relay cannot be reenergized in a simwhen front contact c of relay 3PD opens. The energizple m'annerrWhen this second train proceeds sufficiently far into section 3T to clear loop 18, relay TE is energized by the circuit including front contact 0 of relay 3PD, which then closes, and back contact b of relay TES. The timing period of relay TE is preset at some desiredlength but, upon energization of its winding, its check back contact b is immediately opened.

Let us assume now that both trains clear section 3T so 'that relay 3TR again receives code pulses and relays 3TFP and 3H shortly pick up, the latter after a brief delay required by its slow pick up characteristics. Relay 3RC then follows the code pulses and causes the transmission of the reverse code. When loop 18 was previously cleared, the proximity detector responded to the absence of any train and relay lAP was energized and picked up in the manner previously described. If a third train now enters section 1T, relay lAP again releases but no cab signal energy is applied, even with relay 3H picked up, since the circuit for supplying energy to the primary of transformer CS is now open at front contact c of relay TES and also at checking back contactb of relay TE. This open circuit condition continues until the timing period of relay TE expires. At this instant, relay TE closes its front contact a and completes the circuit including front contact of relay 3PD to energize the winding of relay TES which then picks up. The closing of front contacts a and b at this time again completes both the first and second stick circuits for relay TES which then holds. However, the opening of back contact b of relay TES deenergizes relay TE which quickly releases, opening its front contact a but again closing its checking back contact b. Upon the completion of this timing action, the previously traced circuit for applying cab signal energy to the primary of transformer CS is again complete so that with relay lAP released, cab signal energy pulses are applied to section IT for any train detected approaching through that section at that moment. This timing operation protects against a loss of shunt under a second train moving through section 3T which might be long enough to allow relay 3H to pick up in its usual decoding operation. However, front contact b of relay 3H, upon closing, cannot complete the circuit from terminal BX during the timing operation since both front contact 6 of 35 relay TES and the checking back contact b of relay TE are open. The second train is thus provided sufficient time to clear section 3T at restricted speed or to provide protection against the following train before cab signal energy can be applied for such a following train moving in section 1T.

As previously mentioned, it is to be understood that these additional protection features, that is, the proximity detector and the timing delay arrangement, may be deleted from the circuit arrangement of H6. 3 if not needed. The arrangement then functions as a cab signal only, check-in, check-out signaling system with a one block overlap spacing in the application of cab signal energy to following trains. Such circuits can be envisioned by considering the circuit diagram illustrated without contacts of relays 3PD, 3PDP, TES, and TE in the various circuit paths. The proximity detector train detection check may be added alone without the timing delay if assurance against the loss of shunt under the rear cars of the train is desired. Specifically, the proximity detection would then protect against the loss of shunt with one or more rear cars of the train still occupying section 1T. Obviously wayside signals with additional indications in the manner of FIG. 2 may be added to the arrangement of FIG. 3 with or without the additional protection features. This would provide both cab signal and wayside signal indications for train operation. Additional cab signal indications may be added in any manner known in the art, preferably of course by adding additional code rates to the arrangement. Further, the proximity detector and timing detection separately or together may be added to the coded wayside signal system shown in FIG. 2 if it seems desirable.

Using conventional or standard apparatus, the arrangement of my invention thus provides additional protection against the loss of shunt in, or failure to shunt, a track circuit by a train moving along a track where a signaling system is in service. This protection is accomplished principally by a simple check-in, check-out operation which inhibits the clearing of the track circuit, once train occupancy is registered, until occupancy by that train of the next section in advance along the track stretch is positively registered. Only a little additional apparatus and circuits are required. The arrangement or principles can be used with .line circuit controlled or coded track signaling systems. Particularly in the latter type arrangement, the signaling systems may be either those providing wayside signals or cab signals only or a combination of both. Additional protection can be superposed where the characteristics of the trains and/or the signal system operation require specific detection of the rear of the train at junction locations and timing delay prior to the ad vance of following trains under predetermined conditions. The result is an efficient, simple, and economical circuit arrangement for protecting against the loss of shunt under a train or the failure of a train to shunt the track, especially in the vicinity of the junction between adjoining track sections.

Although I have herein shown and described but three specific embodiments of signaling 'systems embodying the principles of my invention, it is'to 'be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having now described my invention, what I claim as new and desire to serve by Letters patent is:

l. A train detection arrangement for a stretch of railroad track including an approach section adjoining an advance section, through which trains move in that order, comprising,

a. a first relay coupled to the rails of each section at the junction between said adjoining approach and advance sections and selectively responsive for detecting the occupancy of the corresponding section by a train,

b. a second relay for each section controlled by the associated first relay for registering an occupied condition of the corresponding section when a train is detected by said associated first relay,

. an occupancy registration clearing circuit network jointly controlled by an unoccupied condition contact of the approach section second relay and an occupied condition contact of the advance section second relay and coupled to said approach section second relay for retaining a train occupancy registration for said approach section, after a train clears that section, until that train is registered as occupying said advance section.

2. A train detection arrangement as defined in claim 1 in which,

a. each first relay is a track relay connected for normally receiving operating energy through the rails of the corresponding section when that section is unoccupied by any train,

b. said approach section second relay normally repeats the operated condition of the associated first relay and is normally energized by a stick circuit also including its own repeating position contact,

1. said approach section second relay releasing to register and retain a second occupancy detection when said associated first relay initially remains in its non-operated condition,

0. said advance section second relay repeats the operated condition of the associated first relay, releasing to register the detection of train occupancy of that section, and

d. said occupancy clearing circuit network includes a circiut path over a released position contact of said advance section second relay connected for resetting said approach section second relay to its non-occupancy repeating position only when the same train is positively detected occupying said advance section.

3. In a track circuit arrangement, for detecting trains moving through a stretch of railroad track divided into a plurality of successive sections, at each predeter' mined junction location between adjoining sections, the combination comprising,

a. a first track circuit means coupled to the rails of, and responsive to a train shunt within the section in approach to that junction for registering the occupancy of that section by an approaching train,

b. a second track circuit means coupled to the rails of the section in advance of said junction location and responsive to a train shunt for registering the occupancy of that advance section by said train, and

c. an occupancy clearing circuit network controlled jointly by said first and second track circuit means and connected for restoring said first track circuit means to an unoccupied section registry subsequent to a train shunt only when the occupancy of said advance section by that train has been registered.

4. A track circuit arrangement as defined in claim 3 in which each track circuit means includes,

a. a detector track relay at the junction end coupled to the rails for detecting the presence or absence of a train in the corresponding section,

b. a registry relay controlled by the associated track relay for registering an occupied condition when presence ofa train is detected in the corresponding section,

1 the approach section registry relay also controlled by its own unoccupied contact for at times retaining a section occupied registration subsequent to the approach section track relay again detecting the absence of a train,

c. said clearing circuit network including an occupied condition contact of the advance section registry relay and connected for restoring said approach section registry relay to an unoccupied condition registry when said approach section track relay again detects the absence of a train, only when the occupancy of said advance section by that train has been registered.

5. A track circuit arrangement as defined in claim 3 which further includes,

a. an occupancy condition registry relay at said junction for each adjoining track section, and in which each track circuit means comprises,

b. a coded track circuit network including the rails of the corresponding section and operable for transmitting code pulses alternately in each direction through that section,

c. a code following track relay connected to the rails at each end of said corresponding section and responsive to code pulses transmitted from the other end for detecting the absence or presence of a train in that section as code pulses are received or interrupted, respectively,

d. a decoding circuit means at each end of the section controlled by the associated track relay and connected for actuating the corresponding registry relay to register an unoccupied or occupied condition of that section as code pulses are received by said associated track relay or are interrupted,

e. the decoding means at the exit end of said approach section to said junction also controlled by an unoccupied condition contact of the associated registry relay for retaining an occupied condition registration until said associated registry relay is restored by said clearing circuit network and the associated track relay follows received code pulses,

f. said clearing circuit network including an occupied condition contact of the advance section entrance and registry relay and connected for restoring the approach section exit end registry relay to its nonoccupied condition, when the associated track relay detects the departure of a train from said approach section, only when said entrance end registry relay has registered the occupancy of said advance section by that train.

6. A railroad signal system for controlling the movement of a train from an approach track section into an adjoining advance track section, comprising,

a. a first track circuit means including the rails of said approach section for registering the presence or absence of a train in that section,

b. a second track circuit means including the rails of said advance section for registering the presence or absence of a train in that section,

c. a signal means at the junction between the sections controlled by said second track circuit means for providing a restricted or a proceed indication to direct a train in said approach section to stop or move into said advance section as, respectively, a train presence or absence in the advance section is registered,

d. said signal means further controlled by said first track circuit means for displaying said proceed indication only when a train requiring such indication occupies said approach section,

e. said second track circuit means coupled to said first track circuit means for inhibiting the registration of an unoccupied approach section subsequent to a registered train occupancy of that section until that train is positively registered occupying said advance section, and

f. another signal means controlled by said first track circuit means for inhibiting the entry of a following train into said approach section while a train occupancy registration is retained by said first track circuit means.

7. A signal system as defined in claim 6, in which each track circuit means includes,

a. at least one track relay coupled to the rails for detecting the presence or absence of a train occupying the corresponding section, and

b. a registry relay controlled by the associated track relay for registering the occupancy or nonoccupancy of the corresponding section by a train, and which further includes,

c. a reset circuit network jointly controlled by both registry relays for clearing the track occupancy previously registered by the approach section registry relay after the corresponding train clears the approach section only when the occupancy of said advance section by that train has been registered by the advance section registry relay.

8. A signal system as defined in claim 7 in which said reset circuit network includes,

a. a stick contact of said approach section registry relay to normally retain an unoccupied section registry and to effect retention of an occupancy registry once entered, and

b. a contact of said advance section registry relay closed only when a train occupancy is registered and connected for resetting the approach section registry relay to an unoccupied condition-registration.

9. A signal system as defined in claim 6 in which,

a. said first track circuit means includes an approach track relay at the exit end of said approach section responsive for detecting the absence or presence of a train in that section,

b. said second track circuit means includes a track relay at the entrance end of said advance section responsive for detecting the absence or presence of a train in that section, and which further includes,

c. a signal control relay associated with saidadvance section,

d. a first line circuit means controlled at least by contacts of said advance track relay and connected to said control relay for registering the unoccupied and occupied condition of said advance section,

1 said signal control relay connected for selecting between proceed and restricted indications on said junction signal means as that relay is in its unoccupied and occupied positions, respectively,

. an approach registry relay associated with said approach section,

f. a second line circuit means controlled at least by contacts of said approach track relay and connected to said registry relay for registering the unoccupied and occupied conditions of said approach section,

1 said second line circuit means also including an unoccupied condition stick contact of said registry relay to retain an occupied condition registration subsequent to the departure of the corresponding train, and

g. a reset circuit path connected to said second line circuit means and including an occupied position contact of said signal control relay for completing said second line circuit means to restore said approach registry relay to its unoccupied condition only when the occupancy of said advance section by the train is registered,

h. said second line circuit means also coupled for controlling said second signal means to a proceed indication only when that line circuit means is complete.

10. A signal system as defined in claim 6 in which,

a. each track circuit means is of the coded type transmitting master and reverse code pulses from the exit and entrance ends, respectively, of the corresponding section,

b. said first track circuit means includes an approach track relay at the exit end of said approach section responsive to the reverse code pulses for detecting the absence or presence of an approaching train within that section,

c. said second track circuit means includes a master code track relay at the entrance end of said advance section responsive to the master code pulses for detecting the absence or presence of a train occupying that section, and which further includes,

d. a decoding relay associated with each code following track relay and controlled thereby for normally registering the unoccupied or occupied condition of the corresponding section as detected by the associated track relay,

e. said approach section decoding relay also controlled by the advance section decoding relay for again registering an unoccupied condition when a train clears said approach section only if the occupancy of said advance section by that train has been registered.

11. A signal system as defined in claim 10 which further includes,

a. a decoding circuit means controlled by each track relay and coupled to the associated decoding relay for registering an unoccupied section condition when the associated track relay is receiving code pulses, said associated decoding relay otherwise registering an occupied section condition,

b. the decoding circuit means for said approach section further controlled by an unoccupied condition contact of the associated decoding relay for retaining an occupied section registry after the corresponding train clears the section, and

c. a restoring circuit path including an occupied condition contact of the advance section decoding relay and connected for restoring the approach section decoding relay to its unoccupied condition only when the train is registered occupying the advance section.

12. A signal system as defined in claim 11 in which said signal means at said junction comprises,

a. a source of cab signal energy,

b. a coupling means for at'times coupling said source to the rails of said approach section, and

c. a signaling circuit network controlled by said advance section decoding'i'neans and including an occupied condition contact of said approach section decoding relay and connected between said source and said coupling means for providing a selected cab signal indication to an approaching train.

13. A signal system as defined in claim 12 which further includes,

a. an auxiliary train detector means associated with said advance section and responsive for indicating the absence or presence of any part of a train within a predetermined distance from said junction at the entrance end of said advance section,

b. said auxiliary detection means coupled to said restoring circuit for inhibiting the restoration of an unoccupied condition on said approach section decoding relay if any part of a train is indicated within said predetermined distance in said advance section,

e. each signal control relay connected to the associated wayside signal for selecting a proceed or restricted indication to display to an approaching train as the corresponding section is unoccupied or occupied, respectively,

1 each wayside signal controlled by the approach section approach registry relay for displaying a proceed indication only when an approaching train is registered,

c. said auxiliary detection means also coupled for inhibiting the registry of an unoccupied condition for said advance track section by said advance section decoding relay when a train is within said predetermined distance,

d. said signaling circuit network including an unoccupied condition contact of said advance section decoding relay for inhibiting the applicationof cab signal energy when said advance section is occupied. f. a reset circuit path connected to each line circuit 14. In a stretch of railroad track divided into a series and including an occupied condition contact of the of adjoining sections, a signal system providing operatadvance section signal control relay for completing ing signals to trains traversing the stretch in a predeterthat line circuit to restore the associated approach mined direction, comprising, registry relay to its unoccupied condition only a. a track circuit means for each section coupled to when the occupancy of said advance section by the the section rails for detecting and registering the occupancy of that section by a train, and

b. a signal control means at the junction between each adjoining pair of sections, responsive to the occupancy condition registered by at least the advance section track circuit means for determining the operating signal indication supplied to a train in the adjoining approach section,

c. each track circuit means controlled by the track circuit means of the adjoining advance section for clearing a registered train occupancy only when that train has been detected and a section occupied condition registered by said advance section track circuit means.

15. A signal system as defined in claim 14 which further includes,

a. an approach detection means at the exit end of each section controlled by the corresponding track circuit means for registering the occupancy of the corresponding section by an approaching train,

1 each approach detection means also self controlled for retaining an occupancy registration after the detected train has cleared the corresponding section,

b. each approach detection means further controlled by the adjoining advance section track circuit means for restoring an unoccupied section registration after a train clears that approach section only when that train has been registered as occupying that advance section.

16. A signal system as defined in claim 15 in which each signal control means comprises,

a. a wayside signal at the section juncion for displaying a signal indication to approaching trains, and b. a signal control relay associated with the advance section, and in which,

c. each approach detection means comprises a registry relay, and which further includes,

d. a line circuit means associated with each section, controlled by the corresponding track circuit means and connected to the corresponding signal control relay at the section entrance end and the approach registry relay at the exit end for registering the unoccupied or occupied condition of the associated section as the track circuit means detects the absence or presence of a train within the section,

1 each line circuit including an unoccupied condition contact of the associated approach registry relay for retaining an occupied registration after that train departs from the corresponding section,

same train is registered.

17. A signal system as defined in claim 14 in which each track circuit means comprises,

a. a coded track circuit network including the associated section rails and operable for transmitting code pulses alternately in each direction through that section,

b. a code following track relay connected to the rails at each end of the associated section and responsive tocode pulses transmitted from the other end for detecting the absence or presence of a train within that section, and

c. a decoding circuit means at each end of the section controlled by the associated track relay and including aregistry relay for registering an unoccupied or occupied condition of that section as code pulses are received by the associated track relay or are interrupted,

(1. each exit end decoding circuit means also con- Y trolled by an unoccupied condition contact of the associated registry relay for at times retaining an occupancy registration after the detected train has cleared the section, and which further includes,

e. a clearing circuit network for each exit end registry relay controlled by the corresponding advance section entrance registry relay for restoring the exit registry relay to its unoccupied condition, when the associated track relay again receives code pulses, only when the occupancy of the advance section by that train has been registered,

f. each signal control means controlled by the advance section entrance registry relay for selecting between a proceed and a restricted indication for an approaching train as an unoccupied or an occupied condition is registered, respectively, and by the approach section exit registry relay for displaying the proceed indication when an approaching train is registered.

18. A signal system as defined in claim 17 in which each signal control means comprises,

a. a wayside signal located at the junction between the associated adjoining sections, and

b. a control circuit network connected to the associated wayside signal and jointly controlled by at least the associated advance section entrance end registry relay and by the associated approach section exit registry relay for selecting between a proceed and restricted indication for display as said associated advance section is unoccupied or occupied, respectively, and for activating the display of a proceed signal only when an approaching train is registered.

c. a signaling circuit network including an unoccupied condition contact of the corresponding advance section entrance registry relay and an occupied condition contact of the adjoining approach section exit registry relay for connecting said source to said coupling means. 

1. A train detection arrangement for a stretch of railroad track including an approach section adjoining an advance section, through which trains move in that order, comprising, a. a first relay coupled to the rails of each section at the junction between said adjoining approach and advance sections and selectively responsive for detecting the occupancy of the corresponding section by a train, b. a second relay for each section controlled by the associated first relay for registering an occupied condition of the corresponding section when a train is detected by said associated first relay, c. an occupancy registration clearing circuit network jointly controlled by an unoccupied condition contact of the approach section second relay and an occupied condition contact of the advance section second relay and coupled to said approach section second relay for retaining a train occupancy registration for said approach section, after a train clears that section, until that train is registered as occupying said advance section.
 2. A train detection arrangement as defined in claim 1 in which, a. each first relay is a track relay connected for normally receiving operating energy through the rails of the corresponding section when that section is unoccupied by any train, b. said approach section second relay normally repeats the operated condition of the associated first relay and is normally energized by a stick circuit also including its own repeating position contact,
 3. In a track circuit arrangement, for detecting trains moving through a stretch of railroad track divided into a plurality of successive sections, at each predetermined junction location between adjoining sections, the combination comprising, a. a first track circuit means coupled to the rails of, and responsive to a train shunt within the section in approach to that junction for registering the occupancy of that section by an approaching train, b. a second track circuit means coupled to the rails of the section in advance of said junction location and responsive to a train shunt for registering the occupancy of that advance section by said train, and c. an occupancy clearing circuit network controlled jointly by said first and second track circuit means and connected for restoring said first track circuit means to an unoccupied section registry subsequent to a train shunt only when the occupancy of said advance section by that train has been registered.
 4. A track circuit arrangement as defined in claim 3 in which each track circuit means includes, a. a detector track relay at the junction end coupled to the rails for detecting the presence or absence of a train in the corresponding section, b. a registry relay controlled by the associated track relay for registering an occupied condition when presence of a train is detected in the corresponding section, 1 the approach section registry relay also controlled by its own unoccupied contact for at times retaining a section occupied registration subsequent to the approach section track relay again detecting the absence of a train, c. said clearing circuit network including an occupied condition contact of the advance section registry relay and connected for restoring said approach section registry relay to an unoccupied condition registry when said approach section track relay again detects the absence of a train, only when the occupancy of said advance section by that train has been registered.
 5. A track circuit arrangement as defined in claim 3 which further includes, a. an occupancy condition registry relay at said junction for each adjoining track section, and in which each track circuit means comprises, b. a coded track circuit network including the rails of the corresponding section and operable for transmitting code pulses alternately in each direction through that section, c. a code following track relay connected to the rails at each end of said corresponding section and responsive to code pulses transmitted from the other end for detecting the absence or presence of a train in that section as code pulses are received or interrupted, respectively, d. a decoding circuit means at each end of the section controlled by the associated track relay and connected for actuating the corresponding registry relay to register an unoccupied or occupied condition of that section as code pulses are received by said associated track relay or are interrupted, e. the decoding means at the exit end of said approach section to said junction also controlled by an unoccupied condition contact of the associated registry relay for retaining an occupied condition registration until said associated registry relay is restored by said clearing circuit network and the associated track relay follows received code pulses, f. said clearing circuit network including an occupied condition contact of the advance section entrance and registry relay and connected for restoring the approach section exit end registry relay to its non-occupied condition, when the associated track relay detects the departure of a train from said approach section, only when said entrance end registry relay has registered the occupancy of said advance section by that train.
 6. A railroad signal system for controlling the movement of a train from an approach track section into an adjoining advance track section, comprising, a. a first track circuit means including the rails of said approach section for registering the presence or absence of a train in that section, b. a second track circuit means including the rails of said advance section for registering the presence or absence of a train in that section, c. a signal means at the junction between the sections controlled by said second track circuit means for providing a restricted or a proceed indication to direct a train in said approach section to stop or move into said advance section as, respectively, a train presence or absence in the advance section is registered, d. said signal means further controlled by said first track circuit means for displaying said proceed indication only when a train requiring such indication occupies said approach section, e. said second track circuit means coupled to said first track circuit means for inhibiting the registration of an unoccupied approach section subsequent to a registered train occupancy of that section until that train is positively registered occupying said advance section, and f. another signal means controlled by said first track circuit means for inhibiting the entry of a following train into said approach section while a train occupancy registration is retained by said first track circuit means.
 7. A signal system as defined in claim 6, in which each track circuit means includes, a. at least one track relay coupled to the rails for detecting the presence or absence of a train occupying the corresponding section, and b. a registry relay controlled by the associated track relay for registering the occupancy or non-occupancy of the corresponding section by a train, and which further includes, c. a reset circuit network jointly controlled by both registry relays for clearing the track occupancy previously registered by the approach section registry relay after the corresponding train clears the approach section only when the occupancy of said advance section by that train has been registered by the advance section registry relay.
 8. A signal system as defined in claim 7 in which said reset circuit network includes, a. a stick contact of said approach section registry relay to normally retain an unoccupied section registry and to effect retention of an occupancy registry once entered, and b. a contact of said advance section registry relay closed only when a train occupancy is registered and connected for resetting the approach section registry relay to an unoccupied condition registration.
 9. A signal system as defined in claim 6 in which, a. said first track circuit means includes an approach track relay at the exit end of said approach section responsive for detecting the absence or presence of a train in that section, b. said second track circuit means includes a track relay at the entrance end of said advance section responsive for detecting the absence or presence of a train in that section, and which further includes, c. a signal control relay associated with said advance section, d. a first line circuit means controlled at least by contacts of said advance track relay and connected to said control relay for registering the unoccupied and occupied condition of said advance section, 1 said signal control relay connected for selecting between proceed and restricted indications on said junction signal means as that reLay is in its unoccupied and occupied positions, respectively, e. an approach registry relay associated with said approach section, f. a second line circuit means controlled at least by contacts of said approach track relay and connected to said registry relay for registering the unoccupied and occupied conditions of said approach section, 1 said second line circuit means also including an unoccupied condition stick contact of said registry relay to retain an occupied condition registration subsequent to the departure of the corresponding train, and g. a reset circuit path connected to said second line circuit means and including an occupied position contact of said signal control relay for completing said second line circuit means to restore said approach registry relay to its unoccupied condition only when the occupancy of said advance section by the train is registered, h. said second line circuit means also coupled for controlling said second signal means to a proceed indication only when that line circuit means is complete.
 10. A signal system as defined in claim 6 in which, a. each track circuit means is of the coded type transmitting master and reverse code pulses from the exit and entrance ends, respectively, of the corresponding section, b. said first track circuit means includes an approach track relay at the exit end of said approach section responsive to the reverse code pulses for detecting the absence or presence of an approaching train within that section, c. said second track circuit means includes a master code track relay at the entrance end of said advance section responsive to the master code pulses for detecting the absence or presence of a train occupying that section, and which further includes, d. a decoding relay associated with each code following track relay and controlled thereby for normally registering the unoccupied or occupied condition of the corresponding section as detected by the associated track relay, e. said approach section decoding relay also controlled by the advance section decoding relay for again registering an unoccupied condition when a train clears said approach section only if the occupancy of said advance section by that train has been registered.
 11. A signal system as defined in claim 10 which further includes, a. a decoding circuit means controlled by each track relay and coupled to the associated decoding relay for registering an unoccupied section condition when the associated track relay is receiving code pulses, said associated decoding relay otherwise registering an occupied section condition, b. the decoding circuit means for said approach section further controlled by an unoccupied condition contact of the associated decoding relay for retaining an occupied section registry after the corresponding train clears the section, and c. a restoring circuit path including an occupied condition contact of the advance section decoding relay and connected for restoring the approach section decoding relay to its unoccupied condition only when the train is registered occupying the advance section.
 12. A signal system as defined in claim 11 in which said signal means at said junction comprises, a. a source of cab signal energy, b. a coupling means for at times coupling said source to the rails of said approach section, and c. a signaling circuit network controlled by said advance section decoding means and including an occupied condition contact of said approach section decoding relay and connected between said source and said coupling means for providing a selected cab signal indication to an approaching train.
 13. A signal system as defined in claim 12 which further includes, a. an auxiliary train detector means associated with said advance section and responsive for indicating the absence or presence of any part of a train within a predetermined distance from said junction at the entrance end of said advance section, b. said auXiliary detection means coupled to said restoring circuit for inhibiting the restoration of an unoccupied condition on said approach section decoding relay if any part of a train is indicated within said predetermined distance in said advance section, c. said auxiliary detection means also coupled for inhibiting the registry of an unoccupied condition for said advance track section by said advance section decoding relay when a train is within said predetermined distance, d. said signaling circuit network including an unoccupied condition contact of said advance section decoding relay for inhibiting the application of cab signal energy when said advance section is occupied.
 14. In a stretch of railroad track divided into a series of adjoining sections, a signal system providing operating signals to trains traversing the stretch in a predetermined direction, comprising, a. a track circuit means for each section coupled to the section rails for detecting and registering the occupancy of that section by a train, and b. a signal control means at the junction between each adjoining pair of sections, responsive to the occupancy condition registered by at least the advance section track circuit means for determining the operating signal indication supplied to a train in the adjoining approach section, c. each track circuit means controlled by the track circuit means of the adjoining advance section for clearing a registered train occupancy only when that train has been detected and a section occupied condition registered by said advance section track circuit means.
 15. A signal system as defined in claim 14 which further includes, a. an approach detection means at the exit end of each section controlled by the corresponding track circuit means for registering the occupancy of the corresponding section by an approaching train, 1 each approach detection means also self controlled for retaining an occupancy registration after the detected train has cleared the corresponding section, b. each approach detection means further controlled by the adjoining advance section track circuit means for restoring an unoccupied section registration after a train clears that approach section only when that train has been registered as occupying that advance section.
 16. A signal system as defined in claim 15 in which each signal control means comprises, a. a wayside signal at the section juncion for displaying a signal indication to approaching trains, and b. a signal control relay associated with the advance section, and in which, c. each approach detection means comprises a registry relay, and which further includes, d. a line circuit means associated with each section, controlled by the corresponding track circuit means and connected to the corresponding signal control relay at the section entrance end and the approach registry relay at the exit end for registering the unoccupied or occupied condition of the associated section as the track circuit means detects the absence or presence of a train within the section, 1 each line circuit including an unoccupied condition contact of the associated approach registry relay for retaining an occupied registration after that train departs from the corresponding section, e. each signal control relay connected to the associated wayside signal for selecting a proceed or restricted indication to display to an approaching train as the corresponding section is unoccupied or occupied, respectively, 1 each wayside signal controlled by the approach section approach registry relay for displaying a proceed indication only when an approaching train is registered, f. a reset circuit path connected to each line circuit and including an occupied condition contact of the advance section signal control relay for completing that line circuit to restore the associated approach registry relay to its unoccupied condition only when the occupancy of said advance section by tHe same train is registered.
 17. A signal system as defined in claim 14 in which each track circuit means comprises, a. a coded track circuit network including the associated section rails and operable for transmitting code pulses alternately in each direction through that section, b. a code following track relay connected to the rails at each end of the associated section and responsive to code pulses transmitted from the other end for detecting the absence or presence of a train within that section, and c. a decoding circuit means at each end of the section controlled by the associated track relay and including a registry relay for registering an unoccupied or occupied condition of that section as code pulses are received by the associated track relay or are interrupted, d. each exit end decoding circuit means also controlled by an unoccupied condition contact of the associated registry relay for at times retaining an occupancy registration after the detected train has cleared the section, and which further includes, e. a clearing circuit network for each exit end registry relay controlled by the corresponding advance section entrance registry relay for restoring the exit registry relay to its unoccupied condition, when the associated track relay again receives code pulses, only when the occupancy of the advance section by that train has been registered, f. each signal control means controlled by the advance section entrance registry relay for selecting between a proceed and a restricted indication for an approaching train as an unoccupied or an occupied condition is registered, respectively, and by the approach section exit registry relay for displaying the proceed indication when an approaching train is registered.
 18. A signal system as defined in claim 17 in which each signal control means comprises, a. a wayside signal located at the junction between the associated adjoining sections, and b. a control circuit network connected to the associated wayside signal and jointly controlled by at least the associated advance section entrance end registry relay and by the associated approach section exit registry relay for selecting between a proceed and restricted indication for display as said associated advance section is unoccupied or occupied, respectively, and for activating the display of a proceed signal only when an approaching train is registered.
 19. A signal system as defined in claim 17 in which each signal control means comprises, a. a source of cab signal energy having a predetermined characteristic to which train carried signal apparatus is responsive, b. a coupling means for at times coupling said source to the rails of the approach section adjoining the corresponding junction, and c. a signaling circuit network including an unoccupied condition contact of the corresponding advance section entrance registry relay and an occupied condition contact of the adjoining approach section exit registry relay for connecting said source to said coupling means. 